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A high temperature fuel cell stack system, such as a solid oxide fuel cell
system, with an improved balance of plant efficiency includes a thermally
integrated reformer, combustor and the fuel cell stack.

1. A solid oxide fuel cell system, comprising: a solid oxide fuel cell
stack; and a reformer adapted to reform a hydrocarbon fuel to a hydrogen
containing reaction product and to provide the reaction product to the
stack; wherein the reformer is adapted to be heated by at least one of a
stack cathode exhaust, a combustor which is thermally integrated with the
reformer, and at least one of radiative and convective heating from the
stack across a gap between the stack and the reformer.

2. The system of claim 1, further comprising a stack cathode exhaust
conduit which is thermally integrated with the reformer and which is
adapted to heat the reformer using the stack cathode exhaust.

3. The system of claim 2, wherein a first portion the stack cathode
exhaust conduit comprises a space located between the stack and the
reformer, into which space the stack cathode exhaust is provided from the
stack.

4. The system of claim 1, further comprising a combustor which is
thermally integrated with the reformer, and which is adapted to heat the
reformer.

5. The system of claim 4, wherein a stack cathode exhaust conduit is
connected to an inlet of the combustor.

6. The system of claim 4, wherein the combustor shares at least one wall
with the reformer.

7. The system of claim 6, wherein the reformer comprises a catalyst
containing cylinder and the combustor comprises a catalyst containing
tube located in the cylinder core and the combustor tube wall comprises
an inner wall of the reformer cylinder.

8. The system of claim 6, wherein the reformer comprises a catalyst
containing plate shaped reformer which shares one wall with a catalyst
containing plate shaped combustor.

9. The system of claim 6, wherein the reformer is located between the fuel
cell stack and the combustor.

10. The system of claim 4, further comprising a catalytic partial
oxidation reactor adapted to provide hydrogen into the combustor during
system start up.

11. The system of claim 4, further comprising an air heat exchanger,
wherein an outlet of the combustor is connected to a first inlet of the
air heat exchanger, an air inlet conduit is connected to a second inlet
of the air heat exchanger, and a first outlet of the air heat exchanger
is connected to a cathode inlet of the stack.

12. The system of claim 1, wherein the reformer is adapted to be heated by
at least one of radiative and convective heating from the stack across a
gap between the stack and the reformer.

13. The system of claim 12, wherein the gap between the reformer and the
fuel cell stack comprises a cathode exhaust conduit of the fuel cell
stack.

14. The system of claim 13, wherein an outer reformer wall contains fins
which extend into the cathode exhaust conduit and an inner reformer wall
contains fins which extend into the combustor.

15. The system of claim 1, wherein the reformer is adapted to be heated by
two or more of the stack cathode exhaust, the combustor which is
thermally integrated with the reformer, and the at least one of radiative
and convective heating from the stack across the gap between the stack
and the reformer.

16. The system of claim 15, wherein the reformer is adapted to be heated
by the stack cathode exhaust, by the combustor which is thermally
integrated with the reformer, and by the at least one of radiative and
convective heating from the stack across the gap between the stack and
the reformer.

17. The system of claim 1, further comprising: a condenser adapted to
separate water from a stack anode exhaust; an evaporator adapted to
evaporate water to be provided into a stack inlet fuel stream; and a
fuel-steam mixer adapted to mix the evaporated water and the stack inlet
fuel stream.

18. The system of claim 1, further comprising: a desulfurizer fluidly
connected to a fuel inlet of the fuel cell stack; and a water-gas shift
reactor fluidly connected to a fuel outlet of the fuel cell stack;
wherein the desulfurizer and the water-gas shift reactor are thermally
integrated with each other.

19. The system of claim 1, further comprising: a connecting conduit
connecting a fuel inlet of the fuel cell stack with an outlet of the
reformer; a hydrocarbon fuel inlet conduit connected to an inlet of the
reformer; and a hydrocarbon fuel by-pass line fluidly connected to the
fuel inlet of the fuel cell stack, wherein the by-pass line is adapted to
provide unreformed hydrocarbon fuel into the fuel inlet of the fuel cell
stack.

20. The system of claim 1, further comprising: a hydrogen separation
device fluidly connected to the fuel outlet of the stack; a carbon
monoxide separation device fluidly connected to the fuel outlet of the
stack; a hydrocarbon fuel inlet conduit fluidly connected to a fuel inlet
of the stack; and a carbon monoxide recycle conduit, whose inlet is
fluidly connected to an outlet of the carbon monoxide separation device
and whose outlet is fluidly connected to the fuel inlet of the stack.

21. The system of claim 1, further comprising: a PSA separation device
fluidly connected to a fuel outlet of the stack; and a thermal output of
the stack in addition to the fuel outlet is thermally integrated with at
least a first column of the PSA device.

22. A solid oxide fuel cell system, comprising: a solid oxide fuel cell
stack; a first means for reforming a hydrocarbon fuel to a hydrogen
containing reaction product and for providing the reaction product to the
stack; and a second means for heating the first means using at least one
of a stack cathode exhaust, a heat from a combustion reaction, and at
least one of radiative and convective heating from the stack.

23. The system of claim 22, wherein the second means for heating the first
means uses at least two of the stack cathode exhaust, the heat from a
combustion reaction, and the at least one of radiative and convective
heating from the stack.

24. The system of claim 22, wherein the second means for heating the first
means uses the stack cathode exhaust, the heat from a combustion
reaction, and the at least one of radiative and convective heating from
the stack.

25. The system of claim 22, further comprising a third means for receiving
the stack cathode exhaust and a hydrocarbon fuel and for heating the
first means using a combustion reaction of the stack cathode exhaust and
the hydrocarbon fuel during steady state operation of the stack.

26. A solid oxide fuel cell system, comprising: a solid oxide fuel cell
stack; a reformer which is adapted to reform a hydrocarbon fuel to a
hydrogen containing reaction product and to provide the reaction product
to the stack; and a combustor which shares at least one wall with the
reformer.

27. The system of claim 26, wherein the reformer comprises a catalyst
containing cylinder and the combustor comprises a catalyst containing
tube located in the cylinder core and the combustor tube wall comprises
an inner wall of the reformer cylinder.

28. The system of claim 26, wherein the reformer comprises a catalyst
containing plate shaped reformer which shares one wall with a catalyst
containing plate shaped combustor.

29. The system of claim 26, wherein the reformer is located between the
fuel cell stack and the combustor.

30. The system of claim 29, wherein a space between the reformer and the
fuel cell stack comprises a cathode exhaust conduit of the fuel cell
stack.

31. The system of claim 30, wherein an outer reformer wall contains fins
which extend into the cathode exhaust conduit and an inner reformer wall
contains fins which extend into the combustor.

32. A method of operating a solid oxide fuel cell system, comprising:
providing a hydrocarbon fuel and water vapor into a reformer; reforming
the hydrocarbon fuel in the reformer to form a hydrogen containing
reaction product; providing the reaction product into a solid oxide fuel
cell stack during steady state operation of the stack; and heating the
reformer during steady state operation of the stack using at least one of
a stack cathode exhaust, a combustor which is thermally integrated with
the reformer and at least one of radiative and convective heat generated
by the stack.

33. The method of claim 32, wherein the step of heating comprises heating
the reformer with heat from at least two of the stack cathode exhaust,
the combustor and the stack.

34. The method of claim 33, wherein the step of heating comprises heating
the reformer with heat from the stack cathode exhaust, the combustor and
the stack.

35. The method of claim 32, wherein the step of heating comprises heating
the reformer by passing the stack cathode exhaust adjacent to the
reformer.

36. The method of claim 35, further comprising providing the cathode
exhaust into the combustor after passing the stack cathode exhaust
adjacent to the reformer.

37. The method of claim 32, wherein the step of heating comprises heating
the reformer by a combustion of a hydrocarbon fuel and air in the
combustor.

38. The method of claim 37, further comprising: determining if the
reformer requires additional heat for the reforming reaction; and
controlling the combustor heat output based on the step of determining to
provide an desired amount heat from the combustor to the reformer.

39. The method of claim 37, further comprising providing the combustor
exhaust into an air heat exchanger to heat air being provided through the
air heat exchanger into the stack.

40. The method of claim 32, wherein the step of heating comprises heating
the reformer by at least one of radiative and convective heat generated
by the stack.

41. The method of claim 40, wherein a space between the reformer and the
fuel cell stack comprises a cathode exhaust conduit of the fuel cell
stack.

42. The method of claim 32, wherein the combustor heats the reformer by
sharing at least one wall with the reformer.

43. The method of claim 42, wherein the reformer comprises a catalyst
containing cylinder and the combustor comprises a catalyst containing
tube located in the cylinder core and the combustor tube wall comprises
an inner wall of the reformer cylinder.

45. The method of claim 42, wherein the reformer is located between the
fuel cell stack and the combustor.

46. The method of claim 32, further comprising: providing a hydrocarbon
fuel and air into a catalytic partial oxidation reactor; generating
hydrogen in the catalytic partial oxidation reactor; providing the
generated hydrogen into the combustor at system start-up; heating up the
combustor, the reformer and the solid oxide fuel cell stack during system
start-up; and stopping the provision of hydrocarbon fuel and air into the
catalytic partial oxidation reactor once the stack reaches a
predetermined operating temperature.

47. The method of claim 32, further comprising: providing an anode exhaust
from the fuel cell stack into a condenser; separating water from the
anode exhaust in the condenser; providing water into an evaporator;
converting water to steam in the evaporator; and mixing the steam with a
fuel being provided to the fuel cell stack.

48. The method of claim 32, further comprising: providing a hydrocarbon
fuel into a desulfurizer; providing desulfurized hydrocarbon fuel from
the desulfurizer into the fuel cell stack; providing an anode exhaust
from the fuel cell stack into a water-gas shift reactor; and providing
heat from the water-gas shift reactor to the desulfurizer.

49. The method of claim 32, further comprising providing unreformed
hydrocarbon fuel that does not pass through the reformer into the fuel
inlet of the fuel cell stack.

50. The method of claim 32, further comprising starting up the fuel cell
system, wherein starting up the fuel cell system comprises: providing the
solid oxide fuel cell stack at room temperature, wherein anode electrodes
of the solid oxide fuel cells in the stack are reduced from previous
operation; providing a hydrocarbon fuel and an oxidizer into the
combustor; and raising a temperature of the solid oxide fuel cell stack
to an operating temperature using heat from the combustor, such that no
separately stored reducing or inert gases are used to flush the anode
chamber of the solid oxide fuel cells of the stack during the start-up.

51. The method of claim 32, further comprising: providing a fuel and an
oxidizer into the fuel cell stack; generating an anode exhaust stream
from the fuel cell stack while the fuel and the oxidizer are provided
into the fuel cell stack operating in a fuel cell mode; separating at
least a portion of hydrogen from the anode exhaust stream during the fuel
cell mode operation in a hydrogen separation device; separating at least
a portion of carbon monoxide from the anode exhaust stream during the
fuel cell mode operation in a carbon monoxide separation device; and
recirculating at least a portion of the separated carbon monoxide into a
fuel inlet gas stream.

52. The method of claim 32, further comprising: operating the fuel cell
stack in a fuel cell mode; separating hydrogen from an anode exhaust
stream of the stack using a PSA hydrogen separation device; and heating a
first column of the PSA hydrogen separation device under purge using
another thermal output of the fuel stack in addition to the anode exhaust
stream.

Description

[0001] This application claims benefit of priority of U.S. provisional
application 60/537,899 filed on Jan. 22, 2004 and 60/552,202 filed on
Mar. 12, 2004, both of which are incorporated herein by reference in
their entirety.

BACKGROUND OF THE INVENTION

[0002] The present invention is generally directed to fuel cells and more
specifically to high temperature fuel cell systems and their operation.

[0003] Fuel cells are electrochemical devices which can convert energy
stored in fuels to electrical energy with high efficiencies. High
temperature fuel cells include solid oxide and molten carbonate fuel
cells. These fuel cells may operate using hydrogen and/or hydrocarbon
fuels. There are classes of fuel cells, such as the solid oxide
regenerative fuel cells, that also allow reversed operation, such that
oxidized fuel can be reduced back to unoxidized fuel using electrical
energy as an input.

BRIEF SUMMARY OF THE INVENTION

[0004] The preferred aspects of present invention provide a high
temperature fuel system, such as a solid oxide fuel cell system, with an
improved balance of plant efficiency. The system includes a thermally
integrated unit including a reformer, combustor and the fuel cell stack.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIGS. 1, 2 and 7 are schematics of fuel cell systems according to
preferred embodiments of the present invention.

[0006] FIGS. 3 and 6 are schematics of PSA gas separation devices
according to the preferred embodiments of the present invention.

[0007] FIG. 4 is a schematic of a fuel cell system according to the fifth
preferred embodiment of the present invention.

[0008] FIG. 5 shows the details of the system of FIG. 4.

[0009] FIGS. 8A and 8B are schematics of integrated cylindrical reformer,
combustor and stack unit for a system with two stacks.

[0010] FIGS. 9A and 9B are schematics of integrated plate type reformer,
combustor and stack unit for a system with two stacks.

[0011] FIGS. 10A and 10B are schematics of integrated plate type reformer,
combustor and stack unit for a single stack system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] FIG. 1 illustrates a fuel cell system 1 according to the preferred
embodiments of the present invention. Preferably, the system 1 is a high
temperature fuel cell stack system, such as a solid oxide fuel cell
(SOFC) system or a molten carbonate fuel cell system. The system 1 may be
a regenerative system, such as a solid oxide regenerative fuel cell
(SORFC) system which operates in both fuel cell (i.e., discharge) and
electrolysis (i.e., charge) modes or it may be a non-regenerative system
which only operates in the fuel cell mode.

[0013] The system 1 contains a high temperature fuel cell stack 3. The
stack may contain a plurality of SOFCs, SORFCs or molten carbonate fuel
cells. Each fuel cell contains an electrolyte, an anode electrode on one
side of the electrolyte in an anode chamber, a cathode electrode on the
other side of the electrolyte in a cathode chamber, as well as other
components, such as separator plates/electrical contacts, fuel cell
housing and insulation. In a SOFC operating in the fuel cell mode, the
oxidizer, such as air or oxygen gas, enters the cathode chamber, while
the fuel, such as hydrogen or hydrocarbon fuel, enters the anode chamber.
Any suitable fuel cell designs and component materials may be used.

[0014] The system 1 contains any one or more of the following elements,
either alone or in any suitable combination. In a first embodiment, the
system 1 contains a desulfurizer 5 and a water-gas shift reactor 7 that
are thermally integrated with each other. The waste heat from the reactor
7 is used to heat the desulfurizer 5 to its operating temperature, thus
reducing or eliminating the need for a separate desulfurizer heater.

[0015] In a second embodiment, the system 1 contains a hydrocarbon fuel
reformer 9 and a hydrocarbon fuel by-pass line 11 fluidly connected to
the fuel inlet 13 of the high temperature fuel cell stack 3. The by-pass
line 11 by-passes the reformer 9 to provide unreformed hydrocarbon fuel
into the fuel inlet 13 of the high temperature fuel cell stack 3 to
control the temperature of the stack 3.

[0016] In a third embodiment, the hydrocarbon fuel reformer 9 is located
separately from but thermally integrated with the high temperature fuel
cell stack 3. A start-up burner 15 is thermally integrated with the
reformer 9. Preferably but not necessarily, a start-up burner 15 effluent
outlet conduit 17 is fluidly connected to an oxidizer inlet 19 of the
high temperature fuel cell stack 3. This configuration allows the system
1 to be started up using only the hydrocarbon fuel and oxidizer without
oxidizing SOFC anode electrodes. This configuration eliminates a
separately stored reducing or inert purge gas that is flushed through the
system to prevent the anode electrodes of the SOFCs from oxidizing.

[0017] In a fourth embodiment, a carbon monoxide separation device 21,
such as pressure swing adsorption (PSA) device is fluidly connected to a
fuel exhaust (i.e., the fuel outlet) 23 of the stack 3. A carbon monoxide
recycle conduit 25 has an inlet that is connected to the outlet of the
carbon monoxide separation device 21 and an outlet that is fluidly
connected to a fuel inlet 13 of the high temperature fuel cell stack 3.
For example, the device 21 allows carbon monoxide to be separately
recirculated into a hydrocarbon fuel inlet conduit 27 of the stack 3 to
enhance the electrochemical reaction in the fuel cells of the stack 3.
Furthermore, since carbon monoxide is recirculated, less carbon monoxide
is provided into the atmosphere than if the carbon monoxide from the
system was simply flared or vented into the atmosphere.

[0018] In a fifth preferred embodiment, a PSA hydrogen separation device
29 is fluidly connected to the fuel exhaust 23 of the stack 3. A thermal
output of the high temperature fuel stack 3 in addition to the fuel
exhaust is thermally integrated with at least a first column of the PSA
device 29 to heat the first column. This use of the stack 3 waste heat to
heat a PSA column under purge allows a reduction in the compression
requirements of the PSA device and/or an increase in the amount of gas
purification for the same level of compression.

[0019] In a sixth preferred embodiment, a solid oxide fuel cell system
with an improved balance of plant efficiency comprises a thermally
integrated reformer, combustor and stack, where the reformer is heated by
the stack cathode exhaust, by radiative and convective heat from the
stack and by the combustor heat during steady state operation. In a
seventh preferred embodiment, the system starts up with hydrogen
generated using a CPOX (catalytic partial oxidation) reactor. In an
eighth preferred embodiment, the system contains an energy efficient and
self sufficient water management subsystem. The system contains at least
one evaporator which uses stack anode exhaust to heat water being
provided into the inlet fuel stream.

I. First Embodiment

[0020] The elements of the system 1 of the first embodiment will now be
described. In prior art systems, organo-sulfur compounds (e.g.,
mercaptans, thiophenes) contained in natural gas fuel are hydrogenated by
adding hydrogen to the fuel inlet stream and reacting the mixture in a
desulfurizer over a suitable catalyst, such as cobalt-molybdenum. The
reaction produces CH.sub.4 and H.sub.2S gases. The H.sub.2S gas is
subsequently removed by reaction with a fixed sorbent bed, containing for
example ZnO or other suitable materials for removing this gas. Usually
these reactions are carried out at about 300.degree. C., and the catalyst
and sorbent can be contained in the same vessel.

[0021] FIG. 1 illustrates an embodiment of a desulfurizer subsystem of the
first embodiment, which comprises the desulfurizer 5 and the water-gas
shift reactor 7 that are thermally integrated with each other.

[0022] The desulfurizer 5 preferably comprises the catalyst, such as
Co--Mo or other suitable catalysts, which produces CH.sub.4 and H.sub.2S
gases from hydrogenated, sulfur containing natural gas fuel, and a
sorbent bed, such as ZnO or other suitable materials, for removing the
H.sub.2S gas from the fuel inlet stream. Thus, a sulfur free or reduced
sulfur hydrocarbon fuel, such as methane or natural gas leaves the
desulfurizer 5.

[0023] The water-gas shift reactor 7 may be any suitable device which
converts at least a portion of the water exiting the fuel cell stack 3
fuel exhaust 23 into free hydrogen. For example, the reactor 7 may
comprise a tube or conduit containing a catalyst which converts some or
all of the carbon monoxide and water vapor in the tail gas exiting
exhaust 23 through a fuel exhaust conduit 31 into carbon dioxide and
hydrogen. The catalyst may be any suitable catalyst, such as an iron
oxide or a chromium promoted iron oxide catalyst. The reactor 7 is
preferably located along conduit 31 between the fuel exhaust 23 and the
PSA hydrogen separation device 29. The reactor 7 works in tandem with the
PSA hydrogen separation device 29 by increasing the amount of free
hydrogen in the fuel side exhaust (i.e., anode exhaust or tail gas) by
converting some water present in the fuel side exhaust gas into hydrogen.
The reactor 7 then provides hydrogen and carbon dioxide to the PSA
hydrogen separation device 29, which separates the hydrogen from the
carbon dioxide. Thus, some of the water present in the fuel may be
converted to hydrogen in the reactor 7.

[0024] The desulfurizer 5 and the water-gas shift reactor 7 are thermally
integrated with each other. This means that waste heat from the reactor 7
is transferred directly or indirectly to the desulfurizer 5. For example,
the desulfurizer 5 and the water-gas shift reactor 7 may be located in
the same hot box such that they are thermally integrated with each other.
Alternatively, the desulfurizer 5 and the water-gas shift reactor 7 may
be located in thermal contact with each other (i.e., in direct physical
contact or by contacting the same thermal mass). Alternatively, the
desulfurizer 5 and the water-gas shift reactor 7 may be connected by a
thermal conduit, such as a pipe containing a thermal transfer fluid, such
as water/steam or another fluid.

[0025] The desulfurizer 5 is fluidly connected to the fuel inlet 13 of the
fuel cell stack 3. The water-gas shift reactor 7 is fluidly connected to
the fuel exhaust 23 of the fuel cell stack. The term fluidly connected
means that the connection may be direct or indirect, as long as a gas or
liquid fluid may be provided through the connection. Preferably, the
desulfurizer 5 is connected to the fuel inlet 13 of the fuel cell stack 3
by the fuel inlet conduit 27. A valve 28 controls the flow of fuel
through conduit 27. The water-gas shift reactor 7 is connected to the
fuel exhaust 23 of the fuel cell stack 3 by the fuel exhaust conduit 31.
It should be noted that the conduits 27 and 31 shown in FIG. 1 contain
several portions or sections that are separated by various processing
devices, such as the desulfurizer 5 and the water-gas shift reactor 7.

[0026] A method of operating the fuel cell system 1 according to the first
embodiment includes providing a hydrocarbon fuel, such as natural gas,
into a desulfurizer 5 from a hydrocarbon fuel source 33, such as a
natural gas supply pipe or a hydrocarbon fuel storage tank or vessel. The
fuel is desulfurized in the desulfurizer 5 and is then provided directly
or indirectly into the fuel cell stack 3 through conduit 27 and inlet 13,
as will be described in more details with respect to the other
embodiments of the present invention.

[0027] The warm fuel exhaust is provided from the fuel cell stack 3
through exhaust 23 and conduit 31 into the water-gas shift reactor 7.
Preferably, the exhaust has given up some of the heat in heat exchangers
and other devices prior to entering the reactor. For example, an optional
fuel heat exchanger and water vaporizer 35 may be provided between the
conduits 27 and 31. The vaporizer 35 humidifies the fuel inlet stream in
conduit 27. The vaporizer 35 can be a device which supplies water vapor
based on cyclic desiccant beds or a rotating desiccant wheel (i.e.,
"enthalpy wheel") and which provides water vapor from an exhaust stream
in conduit 31 into the fuel inlet stream in conduit 27 or the vaporizer
35 can be a steam generator which provides water vapor into the fuel
inlet stream from another water source.

[0028] The warm exhaust gases react with each other according to the
forward water gas shift reaction, CO+H.sub.2O->CO.sub.2+H.sub.2, in
the reactor 7 and give up or provide heat to the desulfurizer 5 side and
the incoming fuel gases passing through it. Preferably, the reactor 7
supplies all of the heat that is needed to operate the desulfurizer 5 at
its standard operating temperature, such as at least about 300.degree.
C., and no other heating means or heaters are used to heat the
desulfurizer 5.

[0029] The hydrogen, carbon monoxide, carbon dioxide and water vapor
containing exhaust continues in conduit 31 to an optional condenser 37,
optional water knockout or separation device 39 and a compressor 41, such
as a reciprocating compressor, to the PSA hydrogen 29 and/or carbon
monoxide 21 separation devices. The water knock out system 39 separates
the water from the fuel exhaust stream and discharges it out of the water
discharge conduit 43 controlled by valve 45, or recirculates it into the
fuel heat exchanger and water vaporizer 35 using a positive displacement
pump 47. The water is preferably provided into the stack 3 when the stack
3 is operated to generate hydrogen while generating little or no
electricity in the fuel cell mode (i.e., no net electricity is produced
in the fuel cell mode), as will be described in more detail below. The
additional water is used to support fuel reforming as needed. An optional
water inlet conduit 49 may also be connected to the water knockout device
39. Additional water may be provided for bootstrapping, as the
electrochemical process will ordinarily generate net water. A flow
control valve 51 position is controlled mechanically or by a computer
dependent on the water level in the water knockout device. The valve 51
controls the amount of water provided into device 39 through conduit 49
based on the water level in the device 39.

II. Second Embodiment

[0030] FIG. 1 illustrates a system 1 of the second embodiment containing
the hydrocarbon fuel by-pass line 11 which allows feeding the fuel cell
stack 3 with an accurately controlled fuel input mixture for improved
control of broad range of operating conditions, such as stack 3 operating
temperature.

[0031] In the prior art, SOFCs are commonly operated with hydrocarbon
fuels, such as methane. The methane may be partially or fully steam
reformed to form hydrogen and carbon oxides before it enters the SOFC
stack. Steam reformation is an endothermic process. If methane is only
partially steam reformed, the remaining methane will be reformed within
the SOFC. The endothermic reaction within the SOFC stack affects the
thermal balance of the SOFC stack.

[0032] Oxidation of hydrocarbons in the high temperature fuel cells
includes an endothermic reaction in which the hydrocarbon fuel, such as
methane or natural gas, is converted to hydrogen and carbon oxides. This
endothermic reaction may not be obvious in the net reaction occurring in
the fuel cell system. One example is a solid oxide fuel cell fed with
methane. In the net reaction, the methane is oxidized to carbon dioxide
and water. However, it is electrochemically highly unlikely for the
methane to be directly oxidized to the products. It is commonly assumed
that some methane first reacts with steam, which is almost always
present, to form hydrogen and carbon oxides. Then the hydrogen and lower
carbon oxides are oxidized. The water formed by the oxidation of hydrogen
can enable steam reformation of yet unconverted methane. The result of
this intermediate chemical reaction is heat consumption at the location
of the steam reformation.

[0033] Heat consumed by reformation inside the fuel cell thereby creates a
cooling effect. This cooling effect can be localized and create
temperature gradients and in turn thermal stresses which can damage part
of the fuel cell. Thus, the reformation is partly or completely performed
outside the fuel cell stack.

[0034] In the system 1 of the second embodiment, the hydrocarbon fuel
reformer 9 is located separately from the high temperature fuel cell
stack 3. The reformer is adapted to at least partially reform a
hydrocarbon fuel into a hydrogen fuel. The hydrocarbon fuel is provided
into the reformer 9 through the hydrocarbon fuel inlet conduit 27,
connected to an inlet of the reformer 9. A connecting conduit 53 connects
the fuel inlet 13 of the high temperature fuel cell stack 3 with an
outlet of the reformer 9.

[0035] The hydrocarbon fuel reformer 9 may be any suitable device which is
capable of partially or wholly reforming a hydrocarbon fuel to form a
carbon containing and free hydrogen containing fuel. For example, the
fuel reformer 9 may be any suitable device which can reform a hydrocarbon
gas into a gas mixture of free hydrogen and a carbon containing gas. For
example, the fuel reformer 9 may reform a humidified biogas, such as
natural gas, to form free hydrogen, carbon monoxide, carbon dioxide,
water vapor and optionally a residual amount of unreformed biogas. The
free hydrogen and carbon monoxide are then provided into the fuel inlet
13 of the fuel cell stack 3 through conduit 53.

[0036] In a preferred aspect of the second embodiment, the fuel reformer 9
is thermally integrated with the fuel cell stack 3 to support the
endothermic reaction in the reformer 9 and to cool the stack 3. The term
"thermally integrated" in this context means that the heat from the
reaction in the fuel cell stack 3 drives the net endothermic fuel
reformation in the fuel reformer 9. The fuel reformer 9 may be thermally
integrated with the fuel cell stack 3 by placing the reformer 9 and stack
3 in the same hot box and/or in thermal contact with each other, or by
providing a thermal conduit or thermally conductive material which
connects the stack 3 to the reformer 9. While less preferred, a separate
heater may also be used to heat the reformer 9 instead of or in addition
to the heat provided from the stack 3.

[0037] The hydrocarbon fuel by-pass line 11 is fluidly connected to the
fuel inlet 13 of the high temperature fuel cell stack 3. In other words,
the by-pass line may be connected directly to the inlet 13 or it may be
indirectly connected to the inlet 13 via the connecting conduit 53. The
terms "line" and "conduit" are used interchangeably, and include gas flow
pipes and other fluid flow ducts. The by-pass line 11 is adapted to
provide unreformed hydrocarbon fuel into the fuel inlet 13 of the high
temperature fuel cell stack 3.

[0038] Preferably, the by-pass line 11 branches off from the hydrocarbon
fuel inlet conduit 27 upstream of the reformer 9 and connects to the
connecting conduit 53 downstream of the reformer 9. Preferably, the
desulfurizer 5 is located upstream of a location where the by-pass line
11 branches off from the hydrocarbon fuel inlet conduit 27, such that
sulfur is removed from the unreformed hydrocarbon fuel provided through
the by-pass line 11.

[0039] Alternatively, the by-pass line 11 does not have to branch off from
the fuel inlet conduit 27. In this case, the by-pass line 11 is connected
to a separate source of hydrocarbon fuel, such as a natural gas pipe or a
storage vessel. In this case, a separate desulfurizer is provided in the
by-pass line 11.

[0040] The system 1 further comprises a hydrocarbon fuel flow control
valve 55 in the by-pass line 11. The control valve 55 is adapted to
control a flow of the unreformed hydrocarbon fuel into the fuel cell
stack to control a temperature and/or other operating parameters of the
fuel cell stack. The valve 55 may be manually or remotely controlled by
an operator. Alternatively, the valve 55 may be automatically controlled
by a computer or other processing device. The valve 55 may be controlled
automatically or by an operator in response to detected or predetermined
parameters. For example, the temperature or other parameters of the fuel
cell stack 3 may be detected by a temperature detector or other
detectors, and the results provided to an operator or a computer. The
operator or computer then adjust the valve 55 to control the flow of the
unreformed hydrocarbon fuel through the by-pass line 11 into the fuel
cell stack 3 to control the fuel cell stack temperature or other
parameters. Alternatively, the by-pass valve 55 may be adjusted based on
predetermined parameters, such as based on time of stack 3 operation that
is stored in the computer memory.

[0041] A method of operating a high temperature fuel cell system 1 of the
second embodiment includes providing a hydrocarbon fuel into a reformer 9
through the fuel inlet conduit 27 and at least partially reforming the
hydrocarbon fuel into hydrogen fuel in the reformer 9. The hydrogen fuel
from the reformer 9 is provided into a fuel inlet of a high temperature
fuel cell stack 3 through conduit 53. The unreformed hydrocarbon fuel
that does not pass through the reformer 9 is provided into the fuel inlet
of the high temperature fuel cell stack 3 through the by-pass line 11 and
optionally through conduit 53. The flow of the unreformed hydrocarbon
fuel through the by-pass line 11 that does not pass through the reformer
9 is controlled by the valve 55 to control a temperature and/or other
operating parameters of the high temperature fuel cell stack 3.

[0042] The oxidation of hydrogen or low carbon oxides inside a fuel cell
is an exothermic reaction. Heat generated by the exothermic oxidation
should be removed to attain stable operation. Unreformed methane can aid
in the removal of heat via the above described steam reformation in the
reformer 9.

[0043] Accurately controlling the amount of unreformed hydrocarbons
entering the stack allows control of the temperature of the fuel cells in
the stack. In an external reformer, the degree of reformation depends on
a variety of factors some of which may vary during operation. Thus, a
simple way of controlling the amount of unreformed hydrocarbons entering
the stack is the by-pass line 11 which by-passes the external reformer 9
as shown in FIG. 1. The bypass valve 55 controls the amount of unreformed
hydrocarbons entering the stack 3. More specifically, the least amount of
hydrocarbons entering the stack 3 is limited by the finite conversion
inside the external reformer. An upper limit for the amount of unreformed
hydrocarbons entering the stack 3 is posed by reformation occurring
outside the external reformer along by-pass line 11.

[0044] This method of the second embodiment is applicable not only to
solid oxide fuel cells, but any high temperature fuel cell fed by a fuel
which undergoes reformation reactions prior to oxidation. In the example
provided above, the reformation is an endothermic reaction, but there are
also reformation reactions that are exothermic. Examples of exothermic
reformation include but are not limited to partial oxidation of methane.
Methane, which is the major constituent of natural gas, is a very common
example of a hydrocarbon fuel that undergoes reformation, but other
hydrocarbon fuels, such as natural gas, propane and butane are possible.
Therefore the reformer by-pass 11 is applicable to various reformation
reactions and a variety of hydrocarbon fuels.

[0045] FIG. 2 illustrates a system 101 of the first and second embodiments
having an alternative configuration from the system 1 shown in FIG. 1. In
the system 101 shown in FIG. 2, the fuel heat exchanger and water
vaporizer 35 is located upstream of the desulfurizer 5. Thus, the fuel
enters the heat exchanger and water vaporizer 35 prior to entering the
desulfurizer. The desulfurizer 5 and the water-gas shift reactor 7 are
located in the same hot box 103 (i.e., a warm box or fuel conditioner).
The fuel conditioner 103 also contains the catalytic start-up burner 15,
the fuel heat exchanger and water vaporizer 35 and an optional fuel
pre-reformer 105 which is thermally integrated with a fuel exhaust heat
exchanger 107. Thus, the catalytic start-up burner 15 in the system 101
is located in the fuel conditioner 103 rather than thermally integrated
with the fuel cell stack 3. The start-up burner 15 is fed by the stack
fuel exhaust conduit 31 rather than by the hydrocarbon fuel inlet conduit
27.

[0046] The fuel cell stack 3 is thermally integrated with the reformer 9
in the same hot box 108. The hot box 108 also contains an optional
radiative air heater 109 and an optional catalytic tail gas burner 110.
The tail gas burner 110 is provided with hydrocarbon fuel from a branch
111 of the hydrocarbon fuel inlet conduit 27, which is regulated by valve
112. A valve 113 directs the fuel exhaust flow between the PSA hydrogen
separation device 29 and the tail gas burner 110. The oxidizer side
components are the same as in system 1 and will be described in more
detail below.

III. Third Embodiment

[0047] FIG. 1 illustrates a system 1 of the third embodiment, where the
system is brought up from room temperature to operating conditions (i.e.,
at start-up) with only hydrocarbon fuel and air. No stored nitrogen or
hydrogen are required to protect the anodes from oxidation. The stack 3,
reformer 9 and start-up burner 15 comprise separate devices which are
thermally integrated with each other, such as being located in the same
hot box and/or being in thermal contact with each other and/or being
connected by a thermal fluid transfer conduit.

[0048] The anodes of SOFC systems are commonly made from materials
including metal oxides which have to be reduced to attain electron
conductivity and thereby enable the electrochemical reaction in the anode
chamber. Metallic oxides used include, but are not limited to nickel
oxide. One common difficulty with these metallic oxides is the necessity
to keep them reduced once they have been reduced. Re-oxidation causes
significant if not catastrophic performance degradation. The prevention
of re-oxidation is a technical challenge for the start-up of a SOFC
system.

[0049] Commonly, the fuel cell anode chamber is flushed with inert or
reducing gases, such as nitrogen or hydrogen, at start-up to prevent
anode electrode re-oxidation. For systems operated on hydrocarbon fuels,
nitrogen or hydrogen are not readily available. Instead one or both gases
are stored separately within or near the system for consumption during
start-up.

[0050] The inventor has realized that a SOFC system can be built and
operated such that the anode can be maintained in its reduced state while
the system is operating only on hydrocarbon fuel and air during start-up.
FIG. 1 illustrates one configuration of a SOFC system 1 according to the
third embodiment.

[0051] As shown in FIG. 1, the start-up burner 15 is thermally integrated
with the reformer 9 and the reformer 9 is thermally integrated with the
stack 3. As discussed above, the term "thermally integrated" includes
location in the same hot box, located in thermal contact with each other
and/or connection by a thermal transfer fluid conduit. The hydrocarbon
fuel inlet conduit 27 is fluidly connected to an inlet of the reformer 9
and to a first inlet of the start-up burner 15 (such as via the burner
fuel delivery conduit 73). A burner oxidizer inlet conduit 57 is
connected to a second inlet of the start-up burner 15. The start-up
burner 15 effluent outlet conduit 17 is fluidly connected to an oxidizer
inlet 19 of the high temperature fuel cell stack 3. For example, the
effluent outlet conduit 17 may be connected directly into the oxidizer
inlet 19 of the stack or it may be connected to an oxidizer inlet conduit
59 which is connected to the oxidizer inlet 19 of the stack 3. The system
also contains an oxidizer blower 61, such as an air blower, which
provides the oxidizer into the burner and stack through the conduits 57
and 59, and an oxidizer exhaust conduit 63 which removes oxidizer exhaust
from the stack 3. The system also contains an optional air filter 65 and
an optional heat exchanger 67 which heats the oxidizer being provided
into the stack 3 through the oxidizer inlet conduit 59 using the heat of
the oxidizer exhaust being provided through the oxidizer exhaust conduit
63. The system also contains valves 69 and 71 in conduits 57 and 59,
respectively. The system also contains a burner fuel delivery conduit 73
which is regulated by valve 75. The conduit 73 branches off from conduit
27 or it may comprise a separate fuel delivery conduit.

[0052] The method of operating the system 1 according to the third
embodiment is as follows. Initially all components of the system are at
room temperature. The anodes of the SOFC stack are reduced from previous
operation. Valves 69 and 75 in conduits 57 and 73, respectively, are
open, while valve 71 in conduit 59 is closed.

[0053] Hydrocarbon fuel, which can be natural gas, and an oxidizer, such
as air or oxygen, are injected into the start-up burner 15 through
conduits 73 and 57, respectfully. The fuel and oxidizer are ignited in
the burner 15 by an ignitor. The heat stream from the combustion in the
burner 15 is directed at the thermally integrated reformer 9. The
effluent of the burner 15 is directed through conduits 17 and 59 into the
oxidizer inlet 19 (i.e., cathode chamber(s)) of the stack 3. The effluent
is exhausted from the stack 3 through conduit 63 and from there into the
air heat exchanger 67. It may be advantageous to operate the burner lean
on fuel to ensure that the cathode chamber(s) of the fuel cells in the
stack are always exposed to an oxidizing environment. The combustion
raises primarily the temperature of the reformer 9, secondarily the stack
3 temperature, and finally the air heat exchanger 67 temperature.

[0054] Fuel is directed through the desulfurizer 5, vaporizer 35 and the
reformer 9, into the stack 3 fuel inlet 13 (i.e., into the anode
chamber(s) of the fuel cells in the stack). The fuel may be directed into
inlet 13 simultaneously with injecting fuel and oxidizer into the burner
15. Alternatively, the fuel may be directed into the inlet 13 after it is
directed into the burner 15 but before the stack 3 reaches the anode
oxidation temperature. The fuel exhaust exits the stack 3 through conduit
31 and water-gas shift reactor 7. The fuel picks up heat in the reformer
9 and in the stack 3 and transports the heat to the water gas shift
reactor 7 which is thermally coupled to the desulfurizer 5. Thereby the
desulfurizer 5 is heated to operating conditions by the stack 3 exhaust,
as provided in the first embodiment. Some heat is also delivered to the
water vaporizer 7.

[0055] The heat balance in the system is designed such that the reformer 9
reaches its operating temperature (i.e., the temperature at which it
reforms the hydrocarbon fuel) before the stack 3 anode chamber(s) reaches
a temperature were re-oxidation of the anode electrodes could occur.
Also, enough heat is carried to the water vaporizer 35 such that the
inflowing fuel is sufficiently humidified to avoid carbon formation in
the hot components downstream of the water vaporizer 35.

[0056] If these method parameters are satisfied, the SOFC anode electrodes
will be exposed to a hydrogen rich feed stream created by steam
reformation in the reformer 9 when a temperature at the anode is reached
at which re-oxidation can occur. At the same time, the desulfurizer 5 is
brought to operating temperature early enough to avoid detrimental
effects of excessive sulfur content in the fuel feed stream. One
preferred hydrocarbon fuel for this system is natural gas. However other
fuels, including but not limited to methane, propane, butane, or even
vaporized liquid hydrocarbons can be utilized.

[0057] After the start-up of the system 1 is completed (i.e., once the
stack reaches desired steady state operating conditions), hydrocarbon
fuel and oxidizer supply into the start-up burner is terminated either by
an operator or automatically by a computer and the start-up burner is
turned off. Valves 69 and 75 are closed and valve 71 is opened to provide
an oxidizer into the oxidizer inlet 19 of the solid oxide fuel cell stack
3. The stack 3 then operates in the fuel cell mode to generate
electricity from an electrochemical reaction of the fuel provided through
conduit 27 and reformer 9 (and optionally through by-pass line 11) and
oxidizer provided through conduit 59. Thus, it should be noted that the
oxidizer is preferably not provided into oxidizer inlet 19 of the solid
oxide fuel cell stack 3 while the start-up burner 15 operates.
Furthermore, no separately stored reducing or inert gases are used to
flush the anode chambers of the solid oxide fuel cells of the stack 3
during the start-up.

IV. Fourth Embodiment

[0058] FIG. 1 illustrates a system 1 of the fourth embodiment, where the
carbon monoxide and hydrogen are separately extracted from the fuel
exhaust stream and recirculated into the fuel inlet stream and/or removed
from the system for other use.

[0059] The system 1 contains a hydrogen separation or purification device
29 fluidly connected to a fuel exhaust 23 of the stack 3. Preferably, the
device 29 comprises a PSA device that is connected to the exhaust 23 of
the stack 3 by the fuel exhaust conduit 31. The PSA device 29 is adapted
to separate at least a portion of hydrogen from the fuel exhaust while
the fuel cell stack 3 generates electricity in a fuel cell mode. A
reciprocating pump 41 provides the fuel exhaust into the PSA device 29.
The hydrogen separation or purification device 29 preferably contains the
carbon monoxide separation device or unit 21 and a carbon dioxide/water
separation device or unit 30. Preferably, the devices 21 and 30 comprise
PSA devices which respectively separate carbon monoxide and carbon
dioxide/water from the fuel exhaust and allow hydrogen to pass through.
Preferably, but not necessarily, the PSA device 21 is located in series
with and downstream from PSA device 30. However, if desired, the PSA
device 21 may be located upstream of PSA device 30. Preferably, PSA
devices 21 and 30 comprise different units of a single PSA system 29,
where each unit 21 and 30 contains at least two PSA columns.

[0060] A carbon monoxide recycle conduit 25 recirculates the carbon
monoxide from the PSA device 21 into the fuel inlet conduit 27. A carbon
dioxide/water removal conduit 26 removes carbon dioxide and water from
device 30. The inlet of conduit 25 is connected to the outlet of the
carbon monoxide separation device 21 and the outlet of conduit 25 is
fluidly connected to the fuel inlet of the high temperature fuel cell
stack 3, such as via the fuel inlet conduit 27. Alternatively, the outlet
of the carbon monoxide recycle conduit 25 may be connected directly into
the reformer 9 and/or into the fuel inlet 13 of the stack 3.

[0061] The system further comprises an optional hydrogen recycle conduit
77 which is controlled by a recirculated hydrogen flow control valve 79.
The inlet of the conduit 77 is connected to the outlet of the hydrogen
separation device 29. The outlet of the conduit 77 is fluidly connected
to the fuel inlet 13 of the high temperature fuel cell stack 3, such as
directly connected to the inlet 13 or indirectly connected via the fuel
inlet conduit 27. If desired, the conduit 77 may be omitted and hydrogen
and carbon monoxide may be carried together through conduit 25, which may
result in a higher purity product or lower compression requirements. If
desired, the flow of hydrogen passed through conduit 25 may be metered.

[0062] Preferably, the outlet of conduits 25 and 77 are merged together
into a recycle conduit 81, which provides the recirculated hydrogen and
carbon monoxide into the fuel inlet conduit 27, as shown in FIG. 1, or
directly into the reformer 9 and/or the stack 3 fuel inlet 13. However,
the recycle conduit 81 may be omitted, and the conduits 25 and 77 may
separately provide carbon monoxide and hydrogen, respectively, into
conduit 27, reformer 9 and/or stack 3 fuel inlet 13. The system 1 also
optionally contains a hydrogen removal conduit 83, which removes hydrogen
from the system 1 for storage or for use in a hydrogen using device, as
will be described in more detail below.

[0063] FIG. 3 illustrates an exemplary two column PSA hydrogen separation
device 29, such as, for example, the carbon dioxide/water separation unit
30 of a larger device or system 29 which also contains the carbon
monoxide separation unit 21 shown in FIG. 1. Preferably, the PSA device
29 operates on a Skarstrom-like PSA cycle. The classic Skarstrom cycle
consists of four basic steps: pressurization, feed, blowdown, and purge.
The device 29 contains two columns 83 and 85. When one column is
undergoing pressurization and feed, the other column is undergoing
blowdown and purge. In one exemplary configuration, the device 29 may be
operated using three three-way valves 87, 89 and 91 and one or more flow
restrictors 93. Of course other configurations may also be used. When the
three-way valves are in the positions shown in FIG. 3, the pressurization
and feed steps are essentially combined, and the blowdown and purge steps
are similarly combined.

[0064] The PSA device 29 operates as follows. A pressurized feed gas (F),
such as the fuel exhaust gas, containing CO.sub.2, H.sub.2O, CO and
H.sub.2 is provided through the fuel exhaust conduit 31. Two-position,
three-way valves 87, 89 and 91 are simultaneously switched to the state
shown in FIG. 3A. The feed is introduced to column 83 via valve 87
pressurizing column 83. The adsorbent contained in column 83 selectively
adsorbs the CO.sub.2 and H.sub.2O. As the feed continues to flow, most of
the H.sub.2 exits as extract (E) via valve 91. The extract may be
provided into conduits 77 and/or 83 shown in FIG. 1, or into the carbon
monoxide PSA device 21 to remove carbon monoxide from the extract. The
device 21 operates in the same way as the portion of the device 29 shown
in FIG. 3, except the bed materials in the columns are selected to
separate hydrogen from carbon monoxide.

[0065] The switching of valve 89 exposes column 85 to a low pressure line,
resulting in the blowdown of column 85. The low pressure line 95 is the
output of column 83 that passes through one or more flow restrictors 93.
Gases that were previously adsorbed during the previous cycle desorb and
flow out through valve 89, producing a desorbate stream (D). The
desorbate stream may be provided into the carbon monoxide PSA device 21
to remove carbon monoxide from the desorbate stream. Meanwhile, a
relatively small quantity of high pressure extract gas flows through the
flow restrictor(s) 93 and through column 85 in the direction opposite to
the feed flow, forming a purge flow that helps remove desorbate from
column 85.

[0066] At a subsequent time, as column 83 approaches saturation, the
positions of all valves are switched. Thus, column 85 becomes the column
fed via valve 87 and is pressurized, and column 83 vents via valve 89 and
blows down. In this way the purity of the extract gas E is maintained.

[0067] A method of operating the system 1 of the fourth embodiment will
now be described. A fuel and an oxidizer are provided into the fuel cell
stack 3 through conduits 27/53 and 59, respectively. A fuel side exhaust
stream is generated from the fuel cell stack 3 through conduit 31 while
the fuel and the oxidizer are provided into the fuel cell stack 3
operating in a fuel cell mode (i.e., while the stack is generating
electricity). At least a portion of the hydrogen is separated from the
fuel side exhaust stream by the PSA hydrogen separation device 29 during
the fuel cell mode operation. For example, the hydrogen and carbon
monoxide are separated from carbon dioxide and water in the PSA carbon
dioxide/water separation device or unit 30. Then, at least a portion of
carbon monoxide is separated from the fuel side exhaust stream (i.e.,
from the hydrogen) in the PSA carbon monoxide separation device or unit
21. At least a portion of the separated carbon monoxide is recirculated
from PSA device 21 through conduits 25 and 81 into the fuel inlet gas
stream in the fuel inlet conduit 27 and/or in conduit 53. The separated
hydrogen from the PSA device 29 may also be recirculated into the fuel
inlet gas stream through conduits 77 and 81, or provided to a hydrogen
storage vessel or to a hydrogen using device 115 outside the system 1
through conduit 83, or both. The valve 79 may be used to determine the
portion of the separated hydrogen being provided through conduits 77 and
83.

V. Fifth Embodiment

[0068] FIGS. 1 and 4 illustrate a system 1 of the fifth embodiment, which
utilizes hydrogen separation from the fuel exhaust stream using
temperature-assisted pressure swing adsorption. In this system, the fuel
cell stack 3 thermal output and the PSA hydrogen separation device 29 are
thermally integrated. In FIG. 4, the carbon dioxide/water separation unit
30 of the device 29 is illustrated for clarity.

[0069] A high temperature fuel cell system 1, such as a SOFC system,
produces hydrogen by way of hydrocarbon reforming reactions that occur
within the stack 3 and/or within the reformer 9. The hydrogen appears in
the system's tailgas (i.e., the stack exhaust), and can be effectively
separated and purified in a pressure-swing adsorption (PSA) device 29.
The gas compression costs associated with the PSA process can be
considerable. The process of the fifth embodiment takes advantage of heat
available from the other parts of the system 1 to reduce those
compression costs.

[0070] The PSA device 29 operates with a pressure differential between its
pressurization/loading and blow-down/purge steps. The pressure
differential, and the associated change in loading of the adsorbed gases,
produces the gas separation. Generally, the higher the pressure
differential, the more effective the separation and the less amount of
purge gas required. As shown in the example of FIG. 3, the product gas is
typically used as the purge gas, and so its use often needs to be
minimized. Typically, the pressure ratio of the pressurization to purge
steps is approximately 10:1, and approximately 10 to 20% of the product
gas is lost as purge.

[0071] The SOFC stack 3 often operates at pressures near ambient, and thus
the fuel exhaust or tailgas containing hydrogen is also near ambient. In
a typical non-thermally integrated design, in order to reach pressures
effective for PSA, the tailgas should be compressed by about a factor of
10. This pressurization is usually not an issue for hydrogen production
plants that use steam methane reforming, because they often operate at
about 10 atmospheres pressure or above.

[0072] If heat is provided during purging steps and removed during loading
steps, the separation process can be made more effective. This would
allow a lower level of compression to be used to achieve a similar
separation objective. Alternatively, a higher degree of purification may
be achieved for the same level of compression. This can occur because the
loading of a adsorbed gas is a strong function of temperature as well as
pressure.

[0073] In many separation systems it is not cost-effective to produce and
remove this heat. In a high temperature fuel cell system, such as a SOFC
system, however, heat of an adequate quality is readily available.

[0074] In one example shown in FIG. 4, warm exhaust air from the stack 3
flowing through oxidizer exhaust conduit 63 is used to heat a PSA column
under purge 85, and cool inlet air flowing through the oxidizer inlet
conduit 59 is used to cool a column 83 under load.

[0075] In another example, a coolant fluid may circulate between the stack
3 operating at an elevated temperature and the PSA separation system 29
through a circulation conduit. The fluid removes excess heat from the
stack 3 and carries it to the separation system 29, where it is used to
heat the gas used to purge the columns. There are a wide variety of ways
to achieve these effects using the various heat sources available in a
high temperature fuel cell system, such as a SOFC system.

[0076] Thus, in the system of the fifth embodiment, the compression
requirements for a pressure-swing adsorption separation system for
hydrogen are reduced by using waste heat from a SOFC stack to effect a
more efficient separation. Alternatively, a higher degree of purification
may be achieved for the same level of compression. In other words, the
extract purity is improved if the column being purged could be heated
with heat originating from a high temperature fuel cell stack, and the
column being fed could be cooled. Alternatively, the pressure of the feed
gas might be reduced, or the amount of purge gas might be reduced, while
the extract purity was maintained. The benefits of this method are
reduced capital equipment costs associated with compression and/or higher
product value associated with higher purity.

[0077] While the method of fifth embodiment was described with respect to
the carbon dioxide/water separation unit 30 of the PSA hydrogen
separation device 29, it may also be used with the PSA carbon dioxide
separation device or unit 21 in addition to or instead of the carbon
dioxide/water separation unit 30. In this case, the waste heat from the
high temperature fuel cell system is used to heat the column under purge
in the carbon monoxide separation device 21 in addition to or instead of
the column under purge in the carbon dioxide/water separation unit 30.
This may be accomplished by providing heat from the oxidizer exhaust
conduit 63 to the column under purge in device 21 and/or by providing
heat from the coolant fluid in the circulation conduit. If desired, the
column under load in the device 21 may be cooled by the cool inlet air
flowing through the oxidizer inlet conduit 59.

[0078] Since each column of the PSA devices 21 and 29 is alternated
between being the column under load and column under purge, the oxidizer
inlet conduit 59 and the oxidizer exhaust conduit 63 are thermally
integrated with all columns of each applicable PSA device 21 and/or 29,
as shown in FIG. 5. For example, each conduit 59, 63 may be split into as
many parallel branches as there are columns in the respective PSA device.
Each branch 59A, 59B, 63A, 63B of the respective conduit 59, 63 is
thermally integrated with a respective column 83, 85, of the PSA 29
device. The flow of cool or hot air through each branch is controlled by
a valve 88. In other words, each PSA device column 83 and 85 is thermally
integrated with a branch 59A, 63A and 59B, 63B of both conduits 59 and
63. However, only cool or warm air is provided to a particular column
depending on if the column is undergoing loading or purging.

[0079] Likewise, if the coolant fluid is circulated between the stack 3
operating at an elevated temperature and the PSA separation system 29
through a circulation conduit, then the circulation conduit is split into
parallel branches, and each branch is thermally integrated with a
respective PSA column. The flow of the coolant fluid is controlled to
each branch by a valve, such that the warm coolant fluid flows only to
those columns that are undergoing purging.

[0080] It should be noted that the term "thermally integrated" in the
context of the fifth embodiment means that the conduit either thermally
contacts the respective PSA column or that it is located adjacent to and
preferably in the same thermal enclosure, such as a hot box or thermal
insulation, as the respective PSA column, to be able to transfer heat to
the column.

[0081] FIG. 6 illustrates an alternative example of a PSA unit 21 or 30 of
the PSA device 29, where all gas flows are decoupled. In the PSA system
shown in FIG. 6, if valves V1, V2 and V3 (numbered 87, 89 and 91 in FIG.
3) are replaced by pairs of two-way valves V1A-V3B (i.e., a two-way valve
would be placed on each horizontal branch stemming from valves V1-V3, and
locations V1, V2 and V3 corresponding to the valves 87, 89 and 91 become
"T" shaped conduit junctions), flow restrictors 93 are replaced by
actuating valves V4A and V4B, and the extract line is valved (V5), then
all flows can be decoupled. In particular, the blowdown/purge steps can
be decoupled and the pressurization/feed steps can be decoupled. This may
have advantages in terms of improvement of purity and reduction of purge
losses, although at the cost of additional equipment. Furthermore, the
lengths of the feed and purge steps can be decoupled. Either can be of
arbitrary length. Clearly this can interrupt the flow of purified
extract, and so occasionally additional beds are provided that increase
the system's flexibility and do not interrupt the flow.

VI. Sixth Embodiment

[0082] The elements of a system 201 of the sixth embodiment will now be
described with respect to FIG. 7. Elements in FIG. 7 with the same
numbers as in FIGS. 1 and 2 should be presumed to be the same unless
noted otherwise. If desired, the system 201 may be used with any one or
more suitable elements of the first, second, third, fourth and/or fifth
embodiments, even if these elements are not explicitly shown in FIG. 7.

[0083] In the sixth embodiment, steam methane reformation (SMR) is used to
preprocess natural gas before it is fed into the stack 3 for
co-generation of hydrogen and electricity from natural gas or other
hydrocarbon fuel using a solid oxide fuel cell system (i.e., a
regenerative or a non-regenerative system). SMR transforms methane to
reaction products comprising primarily carbon monoxide and hydrogen, as
described above. These reaction products are then oxidized in the SOFC
stack 3 at high temperature producing electricity. Excess hydrogen is
retrieved as a side product. Steam methane reformation reactions are
endothermic reactions which require heat, while oxidation reactions in
SOFC stack 3 are exothermic reactions which generate heat. This provides
a synergy for tight heat integration to improve overall Balance of Plant
(BOP) energy efficiency. By integration of reformer 9 and stack 3 in the
hot box 108, heat from the stack 3 can be transferred to the reformer 9
using convective, radiative and/or conductive heat transfer.

[0084] In system 1 illustrated in FIG. 1, the reformer 9 is thermally
integrated with the stack 3 for heat transfer from the stack 3 to the
reformer 9. The stack 3 generates enough heat to conduct the SMR reaction
in the reformer 9 during steady-state operation of the system 1. However,
under some different operating conditions ranging from low to high stack
efficiency and fuel utilization, the exothermic heat generated by the
stack 3 and provided to the reformer 9 may be in greater than, the same
as or less than the heat required to support the steam methane reforming
reaction in the reformer 9. The heat generated and/or provided by the
stack 3 may be less than required to support steam reformation in the
reformer 9 due to low fuel utilization, high stack efficiency, heat loss
and/or stack failure/turndown. In this case, supplemental heat is
supplied to the reformer 9.

[0085] In a preferred aspect of the sixth embodiment, the system 201
provides the supplemental heat to the reformer 9 to carry out the SMR
reaction during steady state operation. The supplemental heat may be
provided from a burner 15 (more generally referred to in this embodiment
as a combustor) which is thermally integrated with the reformer 9 and/or
from a cathode (i.e., air) exhaust conduit which is thermally integrated
with the reformer 9. While less preferred, the supplemental heat may also
be provided from the anode (i.e., fuel) exhaust conduit which is
thermally integrated with the reformer. Preferably, the supplemental heat
is provided from both the combustor 15 which is operating during steady
state operation of the reformer (and not just during start-up) and from
the cathode (i.e., air) exhaust of the stack 3. Most preferably, the
combustor 15 is in direct contact with the reformer 9, and the stack
cathode exhaust conduit 203 is configured such that the cathode exhaust
contacts the reformer 9 and/or wraps around the reformer 9 to facilitate
additional heat transfer. This lowers the combustion heat requirement for
SMR.

[0086] Preferably, the reformer 9 is sandwiched between the combustor 15
and one or more stacks 3 to assist heat transfer, as illustrated in FIGS.
8-10 and as described in more detail below. The combustor 15, when
attached to the reformer 9, closes the heat balance and provides
additional heat required by the reformer. When no heat is required by the
reformer, the combustor unit acts as a heat exchanger. Thus, the same
combustor (i.e., burner) 15 may be used in both start-up and steady-state
operation of the system 201. When using combustion catalysts coated on
the conduit walls, natural gas is preferably introduced at several places
in the combustion zone to avoid auto ignition and local heating.

[0087] Preferably, one or more sensors are located in the system 201 which
are used to determine if the reformer requires additional heat and/or how
much additional heat is required. These sensors may be reformer
temperature sensor(s) which measure the reformer temperature and/or
process parameter sensor(s), which measure one or more of fuel
utilization, stack efficiency, heat loss and stack failure/turndown. The
output of the sensor(s) is provided to a computer or other processor
and/or is displayed to an operator to determine if and/or how much
additional heat is required by the reformer. The processor or operator
then controls the combustor heat output based on the step of determining
to provide an desired amount heat from the combustor to the reformer. The
combustor heat output may be controlled by controlling the amount of fuel
and air being provided into the combustor or by shutting off the fuel
and/or air being provided into the combustor. The combustor may be
controlled automatically by the processor or manually by operator
actions.

[0088] Preferably, the combustor 15 exhaust is provided into the inlet of
the air heat exchanger 67 through conduit 205 to heat the air being
provided into the stack 3 through the exchanger 67. Thus, the stack
cathode exhaust is provided to the exchanger 67 indirectly through the
combustor 15. The configuration of system 201 differs from that of system
1 illustrated in FIG. 1 where the stack cathode exhaust is provided
directly into the exchanger 67 through conduit 63.

[0089] The reformer 9 is located in close proximity to the stack 3 to
provide radiative and convective heat transfer from the stack 3 to the
reformer. Preferably, the cathode exhaust conduit 203 of the stack 3 is
in direct contact with the reformer 9 and one or more walls of the
reformer 9 may comprise a wall of the stack cathode exhaust conduit 203.
Thus, the cathode exhaust provides convective heat transfer from the
stack 3 to the reformer 9.

[0090] Furthermore, if desired, the cathode exhaust from the stack may be
wrapped around the reformer 9 by proper ducting and fed to the combustion
zone of the combustor 15 adjacent to the reformer 9 before exchanging
heat with the incoming air in the external air heat exchanger 67, as
shown in FIGS. 8-10 and as described in more detail below. Natural gas or
other hydrocarbon fuel can be injected and mixed with cathode exhaust air
in the combustion zone of the combustor 15 to produce heat as needed.

[0091] FIGS. 8-10 illustrate three exemplary configurations of the stack,
reformer and combustor unit in the hot box 108. However, other suitable
configurations are possible. The reformer 9 and combustor 15 preferably
comprise vessels, such as fluid conduits, that contain suitable catalysts
for SMR reaction and combustion, respectively. The reformer 9 and
combustor 15 may have gas conduits packed with catalysts and/or the
catalysts may be coated on the walls of the reformer 9 and/or the
combustor 15.

[0092] The reformer 9 and combustor 15 unit can be of cylindrical type, as
shown in FIG. 8A or plate type as shown in FIGS. 9A and 10A. The plate
type unit provides more surface area for heat transfer while the
cylindrical type unit is cheaper to manufacture.

[0093] Preferably, the reformer 9 and combustor 15 are integrated into the
same enclosure and more preferably share at least one wall, as shown in
FIGS. 8-10. Preferably, but not necessarily, the reformer 9 and combustor
15 are thermally integrated with the stack(s) 3, and may be located in
the same enclosure, but comprise separate vessels from the stack(s) 3
(i.e., external reformer configuration).

[0094] In a preferred configuration of the system 201, fins 209 are
provided in the stack cathode exhaust conduit 203 and in the burner 15
combustion zone 207 to assist with convective heat transfer to the
reformer 9. In case where the reformer 9 shares one or more walls with
the cathode exhaust conduit 203 and/or with the combustion zone 207 of
the burner 15, then the fins are provided on the external surfaces of the
wall(s) of the reformer. In other words, in this case, the reformer 9 is
provided with exterior fins 209 to assist convective heat transfer to the
interior of the reformer 9.

[0095] FIGS. 8A and 8B show the cross-sectional top and front views,
respectively, of an assembly containing two stacks 3 and a cylindrical
reformer 9 combustor 15 unit 210. The combustion zone 207 of the
combustor 15 is located in the core of the cylindrical reformer 9. In
other words, the combustor 15 comprises a catalyst containing channel
bounded by the inner wall 211 of the reformer 9. In this configuration,
the combustion zone 207 is also the channel for the cathode exhaust gas.
The space 215 between the stacks 3 and the outer wall 213 of the reformer
9 comprises the upper portion of the stack cathode exhaust conduit 203.
Thus, the reformer inner wall 211 is the outer wall of the combustor 15
and the reformer outer wall 213 is the inner wall of the upper portion of
stack cathode exhaust conduit 203. If desired, a cathode exhaust opening
217 can be located in the enclosure 219 to connect the upper portion 215
of conduit 203 with the lower portions of the conduit 203. The enclosure
219 may comprise any suitable container and preferably comprises a
thermally insulating material.

[0096] In operation, a natural gas (and/or other hydrocarbon fuel) and
steam mixture is fed to the lower end of the reformer 9 through conduit
27. The reformed product is provided from the reformer 9 into the stack
anode (fuel) inlet 13 through conduit 53. The spent fuel is exhausted
from the stack through the anode exhaust 23 and conduit 31.

[0097] The air enters the stack through the cathode (air) inlet 19 and
exits through exhaust opening 217. The system 201 is preferably
configured such that the cathode exhaust (i.e., hot air) exists on the
same side of the system as the inlet of the reformer 9. For example, as
shown in FIG. 8B, since the mass flow of hot cathode exhaust is the
maximum at the lower end of the device, it supplies the maximum heat
where it is needed, at feed point of the reformer 9 (i.e., the lower
portion of the reformer shown in FIG. 8B). In other words, the mass flow
of the hot air exiting the stack is maximum adjacent to the lower portion
of the reformer 9 where the most heat is needed. However, the cathode
exhaust and reformer inlet may be provided in other locations in the
system 201. The hot air containing cathode exhaust is preferably but not
necessarily, provided into the combustion zone 207 of the combustor 15
through conduit 203.

[0098] Natural gas is also injected into the central combustion zone 207
of the combustor 15 where it mixes with the hot cathode exhaust. The
circular or spiral fins are preferably attached to the inner 211 and
outer 213 reformer walls to assist heat transfer. Heat is transferred to
the outer wall 213 of the reformer 9 from the stack 3 by convection and
radiation. Heat is transferred to the inner wall 211 of the reformer by
convection and/or conduction from the combustion zone 207. As noted
above, the reformer and combustion catalysts can either be coated on the
walls or packed in respective flow channels.

[0099] FIGS. 9A and 9B show the cross-sectional top and front views,
respectively, of an assembly containing two stacks 3 and a plate type
reformer 9 coupled with a plate type combustor 15. The configuration of
the plate type reformer-combustor unit 220 is the same as the cylindrical
reformer-combustor unit 210 shown in FIGS. 8A and 8B, except that the
reformer-combustor unit 220 is sandwich shaped between the stacks. In
other words, the combustion zone 207 is a channel having a rectangular
cross sectional shape which is located between two reformer 9 portions.
The reformer 9 portions comprise channels having a rectangular cross
sectional shape. The fins 209 are preferably located on inner 211 and
outer 213 walls of the reformer 9 portions. The plate type reformer and
combustion unit 220 provides more surface area for heat transfer compared
to the cylindrical unit 210 and also provides a larger cross-sectional
area for the exhaust gas to pass through.

[0100] FIGS. 10A and 10B show the cross-sectional top and front views,
respectively, of an assembly containing one stack 3 and a plate type
reformer 9 coupled with a plate type combustor 15. Exhaust gas is wrapped
around the reformer 9 from one side. One side of the combustion zone 207
channel faces insulation 219 while the other side faces the reformer 9
inner wall 213.

VII. Seventh Embodiment

[0101] Hot box 108 components, such as the stack 3 and reformer 9 are
heated to a high temperature before starting (i.e., during the start-up
mode) to draw current from the stack as well as produce hydrogen.
Furthermore, the stack is preferably run in a reducing environment or
ambient using hydrogen until the stack heats up to a reasonably high
temperature below the steady state operating temperature to avoid
reoxidation of the anode electrodes. Stored hydrogen can be used for this
process. However, in the seventh preferred embodiment, a small CPOX
(catalytic partial oxidation) unit is used in the start-up mode of the
system, to make the system independent of external source of hydrogen.

[0102] FIG. 7 illustrates the system 201 containing the CPOX unit 223. Any
suitable CPOX device may be used. However, it should be noted that the
CPOX unit may be used during start-up of other suitable SOFC systems,
such as systems 1 and 101 shown in FIGS. 1 and 2, respectively.

[0103] The system 201 preferably also includes a start-up heater 225 for
heating the CPOX unit 223 during start-up and a mixer 227 for mixing air
and a hydrocarbon fuel, such as methane or methane containing natural
gas. The air and fuel are provided into the mixer through conduits 229
and 231, respectively. The mixed air and fuel are provided into the CPOX
unit 223 after being mixed in the mixer 227.

[0104] The CPOX unit 223 produces hydrogen from the air and fuel mix. The
produced hydrogen is sent with excess oxygen and nitrogen through conduit
233 to the reformer 9. The hydrogen passes through the reformer 9, the
stack 3, the fuel heat exchanger 35, the shift reactor 7 and the
condenser unit 37 and is provided to the combustor 15 through conduit
235. The hydrogen is burned in the combustor 15 to heat up the reformer 9
and stack 15. This process is continued until the system heats up to a
certain temperature, such as a temperature at which oxidation of the
anode electrodes is avoided. Then the CPOX unit 223 is stopped or turned
off, and a hydrocarbon fuel, such as natural gas, is injected directly
into the combustor 15 through conduit 73 to continue the heating process.
The combustor 15 is thermally integrated with the reformer 9 and can be
used during the start-up and during steady state operation modes.

VIII. Eighth Embodiment

[0105] FIG. 7 illustrates the system 201 with components configured for
efficient water management. However, it should be noted that the below
described components may also be configured for efficient water
management for other suitable SOFC systems, such as systems 1 and 101
shown in FIGS. 1 and 2, respectively.

[0106] A SOFC system in general can be self sufficient in water. Heat is
required to make steam required for the methane reformation. Water from
anode exhaust may be condensed and recycled back to the system.
Furthermore, water and natural gas may be fed to a heat exchanger for
transferring heat from the anode exhaust. However, under some operating
conditions, the heat recovered from anode exhaust gas may not be
sufficient to evaporate all the water needed in the reformation reaction
as well as to heat the fuel inlet steam mixture to a desired temperature
before feeding this mixture to the reformer. Thus, additional water
heating and management components may be added to the system 201 to
evaporate all the water needed in the reformation reaction as well as to
heat the fuel inlet steam mixture to a desired temperature before feeding
this mixture to the reformer.

[0107] The system 201 shown in FIG. 7 contains an additional evaporator
237, an optional supplemental heater/evaporator 239 and a steam/fuel
mixer 241. The system operates as follows. The process of steam
generation, mixing steam with fuel, such as natural gas, and preheating
mixture may be done in four steps.

[0108] First, metered water is provided from the condenser 37 through
condensate pump 243, water knockout/tank 39, metering pump 47 and
optional water treatment device 245 into the evaporator 237. The metered
water is heated and at least partially evaporated in the evaporator 237
by the heat from the anode exhaust provided into evaporator from the
shift reactor 7 through conduit 31.

[0109] Second, the partially evaporated water is provided from evaporator
237 into the supplemental heater/evaporator 239. Supplemental heat is
supplied in the heater/evaporator 239 to complete the evaporation process
and superheat the steam.

[0110] Third, the steam is provided from the heater/evaporator 239 into
the steam/fuel mixer 241. The steam is mixed with the fuel in the mixer.

[0111] Fourth, the fuel and steam mix is provided from the mixer 241 into
the fuel heat exchanger 35, where the mix is preheated using heat from
the hot anode exhaust. The fuel and steam mix is then provided into the
reformer through conduit 27.

[0112] Water vapor transfer devices such as enthalpy wheels can be added
to the system to reduce the heat required for the total evaporation
process. These devices can transfer water vapor from the anode exhaust to
incoming fuel stream.

[0113] As described above, the anode exhaust provided into the condenser
37 is separated into water and hydrogen. The hydrogen is provided from
the condenser 37 via conduit 247 into the conduit 31 leading to the
hydrogen purification subsystem 29 and into conduit 235 leading into the
combustor 15. The flow of hydrogen from condenser 37 through conduits 31
and 235 may be controlled by one three way valve or by separate valves
249 and 251 located in conduits 31 and 235, respectively. The hydrogen
from the hydrogen purification system 29 may be provided to the
use/storage subsystem 115 via conduit 83, while the carbon monoxide from
subsystem 29 is provided to the burner or combustor 15 and carbon
monoxide and water from subsystem 29 are exhausted.

[0114] IX. Electricity and Hydrogen Generation

[0115] The electrochemical (i.e., high temperature fuel cell) system of
the preferred embodiments of the present invention such as the solid
oxide electrochemical system, such as a SOFC or a SORFC system, or the
molten carbonate fuel cell system, can be used to co-produce hydrogen and
electricity in the fuel cell mode. Thus, while the prior art SORFC system
can generate either electricity in the fuel cell mode or hydrogen in an
electrolysis mode, the system of the preferred embodiments of the present
invention can co-produce both hydrogen and electricity (i.e., produce
hydrogen and electricity together). The system of the preferred
embodiments generates a hydrogen rich exhaust stream using reforming
reactions that occur within the fuel cell stack and/or in a reformer in
thermal integration with the fuel cell stack. The amount of hydrogen
produced can be controlled by the operator. The hydrogen rich stream is
further conditioned if necessary and stored or used directly by the
operator. Thus, the high temperature electrochemical systems produce
purified hydrogen as a by-product of fuel reformation in the fuel cell
mode. The electrochemical system may operate in the fuel cell mode, when
no external electricity input is required, to generate diffusion of ions
across an electrolyte of the system. In contrast, a reversible or
regenerative electrochemical system operates in the electrolysis mode
when external electricity is required to generate diffusion of ions
across the electrolyte of the system.

[0116] It should be noted that the electrochemical system of the preferred
embodiments does not necessarily co-produce or co-generate power or
electricity for use outside the system. The system may be operated to
primarily internally reform a carbon and hydrogen containing fuel into
hydrogen with minimal power generation or without delivering or
outputting power from the system at all. If desired, a small amount of
power may be generated and used internally within the system, such as to
keep the system at operating temperature and to power system components
in addition to other parasitic loads in the system.

[0117] Thus, in one aspect of the preferred embodiments of the present
invention, the high temperature electrochemical system is a SOFC or a
SORFC system which co-produces electricity and hydrogen in the fuel cell
mode. A SOFC or SORFC system operates in the fuel cell mode when oxygen
ions diffuse through an electrolyte of the fuel cells from the oxidizer
side to the fuel side of the fuel cell containing the carbon and hydrogen
containing gas stream. Thus, when the high temperature electrochemical
system, such as a SOFC or SORFC system operates in the fuel cell mode to
generate hydrogen, a separate electrolyzer unit operating in electrolysis
mode and which is operatively connected to the fuel cell stack is not
required for generation of hydrogen. Instead, the hydrogen is separated
directly from the fuel cell stack fuel side exhaust gas stream without
using additional electricity to operate a separate electrolyzer unit.

[0118] When an SORFC system is used rather than an SOFC system, the SORFC
system can be connected to a primary source of electricity (e.g., grid
power) and can accept electricity from the primary source when desirable
or can deliver electricity to the primary source when desirable. Thus,
when operating the SORFC system of the preferred embodiments, the system
operator does not have to sacrifice electricity production to produce
hydrogen and vice versa. The SORFC system does not require a hot thermal
mass which absorbs heat in the fuel cell mode and which releases heat in
the electrolysis mode for operation or energy storage. However, a hot
thermal mass may be used if desired. Furthermore, the system may use, but
does not require a fuel reformer.

[0119] Furthermore, a relative amount of hydrogen and electricity produced
can be freely controlled. All or a portion of the hydrogen in the fuel
side exhaust stream may be recirculated into the fuel inlet stream to
provide control of the amount of electricity and hydrogen being
co-produced in the system, as will be described in more detail below. The
hydrogen product can be further conditioned, if necessary, and stored or
used directly in a variety of applications, such as transportation, power
generation, cooling, hydrogenation reactions, or semiconductor
manufacture, either in a pressurized or a near ambient state.

[0120] The system 1 or 101 shown in FIGS. 1 and 2 derives power from the
oxidation of a carbon and hydrogen containing fuel, such as a hydrocarbon
fuel, such as methane, natural gas which contains methane with hydrogen
and other gases, propane or other biogas, or a mixture of a carbon fuel,
such as carbon monoxide, oxygenated carbon containing gas, such as
methanol, or other carbon containing gas with a hydrogen containing gas,
such as water vapor, H.sub.2 gas or their mixtures. For example, the
mixture may comprise syngas derived from coal or natural gas reformation.
Free hydrogen is carried in several of the system process flow streams.
The carbon containing fuel is provided into the system from a fuel
source, which may comprise a fuel inlet into the fuel cell stack, a fuel
supply conduit and/or a fuel storage vessel.

[0122] The system 1, 101 and 201 also contains at least one hydrogen
separator, such as the PSA hydrogen separation device 29. The system 1,
101 and 201 also contains an optional hydrogen conditioner 114, as shown
in FIGS. 1 and 2. The hydrogen conditioner 114 may be any suitable device
which can purify, dry, compress (i.e., a compressor), or otherwise change
the state point of the hydrogen-rich gas stream provided from the
hydrogen separator 29. If desired, the hydrogen conditioner 114 may be
omitted.

[0123] The system 1, 101 and 201 also contains a hydrogen storage/use
subsystem 115, as shown in FIG. 2. This subsystem 115 may comprise a
hydrogen storage vessel, such as a hydrogen storage tank, a hydrogen
dispenser, such as a conduit which provides hydrogen or a hydrogen-rich
stream to a device which uses hydrogen, or a hydrogen using device. For
example, the subsystem 115 may comprise a conduit leading to a hydrogen
using device or the hydrogen using device itself, used in transportation,
power generation, cooling, hydrogenation reactions, or semiconductor
manufacture.

[0124] For example, the system 1, 101 and 201 may be located in a chemical
or a semiconductor plant to provide primary or secondary (i.e., backup)
power for the plant as well as hydrogen for use in hydrogenation (i.e.,
passivation of semiconductor device) or other chemical reactions which
require hydrogen that are carried out in the plant.

[0125] Alternatively, the subsystem 115 may also comprise another fuel
cell, such as an SOFC or SORFC or any other fuel cell, which uses
hydrogen as a fuel. Thus, the hydrogen from the system 1, 101 and 201 is
provided as fuel to one or more additional fuel cells 115. For example,
the system 1, 101 and 201 may be located in a stationary location, such
as a building or an area outside or below a building and is used to
provide power to the building. The additional fuel cells 115 may be
located in vehicles located in a garage or a parking area adjacent to the
stationary location. In this case, the carbon and hydrogen containing
fuel is provided to the system 1, 101 and 201 to generate electricity for
the building and to generate hydrogen which is provided as fuel to the
fuel cell 115 powered vehicles. The generated hydrogen may be stored
temporarily in a storage vessel and then provided from the storage vessel
to the vehicle fuel cells 115 on demand (analogous to a gas station) or
the generated hydrogen may be provided directly from the system 1, 101
and 201 to the vehicle fuel cells 115.

[0126] In one preferred aspect of the present invention, the hydrogen
separator 29 is used to separate and route hydrogen from the fuel side
exhaust stream only into the subsystem 115. In another preferred aspect
of the present invention, the hydrogen separator 29 is used to separate
hydrogen from the fuel side exhaust stream and to route all or a part of
the hydrogen back into the fuel inlet 13 of the fuel cell stack 3 through
conduit 81, to route all or part of the hydrogen to the subsystem 115
and/or to route the hydrogen out with the tail gas.

[0127] A preferred method of operating the systems 1, 101 and 201 will now
be described. The systems are preferably operated so that excess fuel is
provided to the fuel cell stack 3. Any suitable carbon containing and
hydrogen containing fuel is provided into the fuel cell stack. The fuel
may comprise a fuel such as a hydrocarbon fuel, such as methane, natural
gas which contains methane with hydrogen and other gases, propane or
other biogas. Preferably, an unreformed hydrocarbon fuel from the by-pass
valve 11 and a hydrogen fuel from the reformer 9 are provided into the
stack 3.

[0128] Alternatively, the fuel may comprise a mixture of a non-hydrocarbon
carbon containing gas, such as carbon monoxide, carbon dioxide,
oxygenated carbon containing gas such as methanol or other carbon
containing gas with a hydrogen containing gas, such a water vapor or
hydrogen gas, for example the mixture may comprise syngas derived from
coal or natural gas reformation. The hydrogen and water vapor may be
recycled from the fuel side exhaust gas stream or provided from hydrogen
and water vapor conduits or storage vessels.

[0129] The reformation reactions occur within the fuel cell stack 3 and/or
in the reformer 9 and result in the formation of free hydrogen in the
fuel side exhaust gas stream. For example, if a hydrocarbon gas such as
methane is used as a fuel, then the methane is reformed to form a mixture
containing non-utilized hydrogen, carbon dioxide and water vapor in the
fuel cell stack 3. If natural gas is used as a fuel, then the natural gas
may be converted to methane in a preprocessing subsystem or it may be
reformed directly to a non-hydrocarbon carbon containing gas such as
carbon monoxide in the reformer 9.

[0130] Preferably, the fraction of hydrogen separated by the hydrogen
separator 29 and the amount of total fuel provided to the fuel cell stack
3 for electricity and hydrogen production are variable and under the
control of an operator operating a control unit of the system. An
operator may be a human operator who controls the hydrogen separation and
electricity production or a computer which automatically adjusts the
amount of hydrogen separation and electricity production based on
predetermined criteria, such as time, and/or based on received outside
data or request, such as a demand for electricity by the power grid
and/or a demand for hydrogen by the subsystem 115. Controlling these two
parameters allows the operator to specify largely independently the
amount of hydrogen produced and the amount of electricity generated. The
outside data or request may comprise one or more of electricity demand,
hydrogen demand, electricity price and hydrogen price, which may be
transmitted electronically to a computer system operator or visually or
audibly to a human system operator.

[0131] In one extreme, when the user of the system needs electricity, but
does not need additional hydrogen, then the operator can choose to have
the hydrogen containing streams recirculated back into the fuel cell
stack 3 by the separator 29 through conduit 81 by opening valve 79, while
providing no hydrogen or a minimum amount of hydrogen to the subsystem
115, through conduit 83, where hydrogen flow may also be controlled by a
valve.

[0132] In another extreme, when the user of the system needs hydrogen, but
does not need any electricity generated, the operator can choose to have
the fuel cell stack 3 act primarily to internally reform the carbon
containing fuel into hydrogen with minimal power generation and/or
minimal or no external power output/delivery from the system. A small
amount of power may be generated to keep the system at operating
temperature and to power the hydrogen separator 29 and conditioner 114,
if necessary, in addition to other parasitic loads in the system. All or
most of the hydrogen from the separator 29 is provided to the subsystem
115 rather than to the conduit 81. In this case, additional water from
the water supply 39 is preferably added to the fuel.

[0133] In the continuum between the two extremes, varying amounts of
hydrogen and electricity may be needed simultaneously. In this case, the
operator can choose to divert varying amounts of the hydrogen from the
separator 29 to conduits 81 and 83, while simultaneously generating the
desired amount of electricity. For example, if more hydrogen is
recirculated back into the fuel cell stack 3 through conduit 81 by
controlling valve 79, then more electricity is generated but less
hydrogen is available for use or storage in the subsystem 115. The trade
off between the amount of electricity and hydrogen produced can vary
based on the demand and the price of each.

[0134] The trade off between the amount of electricity and hydrogen
generated may also be achieved using several other methods. In one
method, the amount of fuel provided to the fuel cell stack 3 is kept
constant, but the amount of current drawn from the stack 3 is varied. If
the amount of current drawn is decreased, then the amount of hydrogen
provided to the hydrogen separator 29 is increased, and vice versa. When
less current is drawn, less oxygen diffuses through the electrolyte of
the fuel cell. Since the reactions which produce free hydrogen (i.e., the
steam-methane reforming reaction (if methane is used as a fuel) and the
water-gas shift reaction) are substantially independent of the
electrochemical reaction, the decreased amount of diffused oxygen
generally does not substantially decrease the amount of free hydrogen
provided in the fuel side exhaust gas stream.

[0135] In an alternative method, the amount of current drawn from the
stack is kept constant, but the amount of fuel provided to the stack 3 is
varied. If the amount of fuel provided to the stack 3 is increased, then
the amount of hydrogen provided to the hydrogen separator 29 is
increased, and vice versa. The amount of fuel may be varied by
controlling the flow of fuel through the fuel inlet conduit 27 by a
computer or operator controlled valve 28 and/or by controlling the flow
of fuel through the by-pass line 11 by valve 55.

[0136] In another alternative method, both the amount of current drawn and
the amount of fuel provided into the fuel cell stack 3 are varied. The
amount of hydrogen generated generally increases with decreasing amounts
of drawn current and with increasing amounts of fuel provided into the
fuel cell stack. The amount of hydrogen generated generally decreases
with increasing amounts of drawn current and with decreasing amounts of
fuel provided into the fuel cell stack.

[0137] Preferably, the systems of the preferred embodiments may be
operated at any suitable fuel utilization rate. Thus, 0 to 100 percent of
the fuel may be utilized for electricity production. Preferably, 50 to 80
percent of the fuel is utilized for electricity production and at least
10 percent, such as 20 to 50 percent, of the fuel is utilized for
hydrogen production. For example, a 100 kWe SOFC system may be used to
generate from about 70 to about 110 kWe of electricity and from about 45
to about 110 kg/day of high pressure hydrogen when 50 to 80 percent of
the fuel is utilized for electricity production. The systems of the
preferred embodiments may be used to produce hydrogen cost effectively.
Thus, the method of the preferred embodiments provides a reduction in the
cost of hydrogen production.

[0138] If the fuel cell stack 3 is a solid oxide regenerative fuel cell
(SORFC) stack which is connected to a primary source of power (such as a
power grid) and a source of oxidized fuel (such as water, with or without
carbon dioxide), then the device can operate transiently in an
electrolysis mode as an electrolyzer to generate hydrogen streams,
methane streams, or mixtures when economically advantageous (e.g., when
the cost of electricity is inexpensive compared to the cost of the fuel
containing bound hydrogen), or during times when the demand for hydrogen
significantly exceeds the demand for electricity. At other times, the
system 1, 101 and 201 can be used in the fuel cell mode to generate
electricity from the stored hydrogen or carbon containing fuel. Thus, the
system 1, 101 and 201 can be used for peak shaving.

[0139] The fuel cell systems described herein may have other embodiments
and configurations, as desired. Other components, such as fuel side
exhaust stream condensers, heat exchangers, heat-driven heat pumps,
turbines, additional gas separation devices, hydrogen separators which
separate hydrogen from the fuel exhaust and provide hydrogen for external
use, fuel preprocessing subsystems, fuel reformers and/or water-gas shift
reactors, may be added if desired, as described, for example, in U.S.
application Ser. No. 10/300,021, filed on Nov. 20, 2002, in U.S.
Provisional Application Ser. No. 60/461,190, filed on Apr. 9, 2003, and
in U.S. application Ser. No. 10/446,704, filed on May 29, 2003 all
incorporated herein by reference in their entirety. Furthermore, it
should be understood that any system element or method step described in
any embodiment and/or illustrated in any figure herein may also be used
in systems and/or methods of other suitable embodiments described above,
even if such use is not expressly described.

[0140] The foregoing description of the invention has been presented for
purposes of illustration and description. It is not intended to be
exhaustive or to limit the invention to the precise form disclosed, and
modifications and variations are possible in light of the above teachings
or may be acquired from practice of the invention. The description was
chosen in order to explain the principles of the invention and its
practical application. It is intended that the scope of the invention be
defined by the claims appended hereto, and their equivalents.